Previous work has established that when fibroblasts or explanted lung tissue are labeled with (14C) proline, approximately 30% of the total (14C) hydroxyproline appears in dialyzable form. The dialyzable hydroxyproline is a product of the intracellular degradation of newly synthesized collagen. The aims of the proposed research are to determine where in the process of collagen biosynthesis this breakdown occurs, how it can be controlled, and how it may vary with the developmental state of the cell. Particular emphasis will be put on exploring the similarities and differences between the intracellular degradation of collagen and the turnover of intracellular proteins. Various steps in the biosynthesis of collagen will be altered using proline analogs, puromycin and fluorouracil, correct triple helical conformation will be altered using hydroxynorvaline; intracellular transport of collagen will also be inhibited. Efforts will be made to alter the amount of degraded collagen by inhibiting intracellular proteases, by changing the nutritional status of the cells and by exposing the cells to hormones. The effect of aging, both in vitro and in vivo, on degradation of collagen will be investigated, as will the dedifferentiation of cells in culture.